Photovoltaic devices are known in the art (e.g., see U.S. Patent Document Nos. 2004/0261841, 2006/0180200, U.S. Pat. Nos. 6,784,361, 6,288,325, 6,613,603, and 6,123,824, the disclosures of which are hereby incorporated herein by reference). Examples of photovoltaic devices include CIGS (Cu(In, Ga)(Se, S)2), CIS (CuInSe2), and a-Si (amorphous silicon) solar cells. The CIGS and CIS films are conductive semiconductor compounds, and these stoichiometries are approximations.
Generally speaking, CIGS and CIS type photovoltaic devices include, from the front or light incident side moving rearwardly, a front substrate of a material such as glass, a front electrode comprising a transparent conductive layer such as a TCO (transparent conductive oxide), a light absorption semiconductor film (e.g., CIGS and/or CIS film), a rear electrode, and a rear substrate of a material such as glass. Sometimes an adhesive is provided between the front substrate and the front electrode, and it is also possible for window layer(s) (e.g., of or including CdS, ZnO, or the like) to be provided. Photovoltaic power is generated when light incident from the front side of the device passes through the front electrode and is absorbed by the light absorption semiconductor film as is known in the art.
However, there exists a need in the art for one or more of: improving efficiency of such photovoltaic devices, reducing the cost of such photovoltaic devices, and/or improving durability of such photovoltaic devices. Thus, it will be appreciated that there exists a need in the art for an improved photovoltaic device that can solve or address one or more of the aforesaid problems.
In certain example embodiments of this invention, a rear electrically conductive electrode comprising Mo (molybdenum) is provided. The Mo inclusive rear electrode is formed in a manner so that its major surface to be closest to the light absorption semiconductor film is textured (roughened) in a substantially controlled and desired manner. In certain example embodiments, the interior surface of the rear glass substrate is textured (roughened) via acid etching, ion beam treatment, or the like. Then, the Mo inclusive rear electrode is formed on the textured surface of the rear glass substrate in a manner so that the major surface of the rear electrode to be closest to the light absorption semiconductor film is also textured. In certain example embodiments, the textured major surface of the rear electrode to be closest to the light absorption semiconductor film may be substantially conformal to the textured surface of the rear glass substrate.
The textured interior surface of the rear electrode is advantageous in several example respects. The textured surface of the rear electrode improves adhesion between the rear electrode and the semiconductor film. Moreover, the textured surface of the rear electrode allows the rear electrode to act as a scattering back electrode thereby permitting it to reflect incident light more effectively and efficiently into the light absorption semiconductor film. This can allow one of both of: improved efficiency of the photovoltaic device, and/or reduced thickness of the light absorption semiconductor film without sacrificing solar efficiency.
In certain example embodiments, after the rear electrode has been formed on the rear glass substrate, the major surface of the rear electrode to be closest to the light absorption semiconductor film may be textured via one or more of ion beam treatment, plasma exposure, and/or a wet chemical etch such as HCl, nitric acid, acetic acid or a combination thereof. This post-deposition texturing (roughening) of the rear electrode surface may, or may not, be used in combination with embodiments where the rear glass substrate is textured. Thus, when the rear electrode is textured (roughened) after the deposition thereof, the rear glass substrate may or may not be textured.
The textured rear glass substrate and/or textured rear electrode (which also functions as a reflector) may be used in a photovoltaic device (e.g., CIS or CIGS solar cell) where an active semiconductor film is provided between the rear electrode/reflector and a front electrode(s).
In certain example embodiments of this invention, there is provided a photovoltaic device comprising: a front substantially transparent conductive electrode; a semiconductor film; a conductive and reflective rear electrode comprising Mo; a rear glass substrate that supports at least the rear electrode comprising Mo; and wherein a surface of the rear glass substrate closest to the semiconductor film is textured so as to have peaks and valleys defined therein, and the rear electrode comprising Mo is provided on the rear glass substrate over the peaks and valleys defined in the rear glass substrate so that the rear electrode comprising Mo also has peaks and valleys defined in a surface thereof closest to the semiconductor film.
In certain example embodiments of this invention, there is provided photovoltaic device comprising: a front substrate; a front substantially transparent conductive electrode; an active semiconductor film; a conductive and reflective rear electrode; a rear glass substrate that supports at least the rear electrode; and wherein the rear electrode comprises a first layer comprising Ti and/or Cr and a second conductive layer comprising Mo provided on the rear glass substrate over at least the first layer, so that the first layer comprising Ti and/or Cr is located between the rear glass substrate and the second layer comprising Mo.
In certain example embodiments of this invention, there is provided a photovoltaic device comprising: a front substrate; a front substantially transparent conductive electrode; an active semiconductor film; a conductive and reflective rear electrode; a rear glass substrate that supports at least the rear electrode; and wherein the rear electrode comprises a layer comprising Mo that is oxidation graded, continuously or discontinuously, so as to be more metallic at a location therein closer to the semiconductor film than at a location therein closer to the rear glass substrate.
In certain example embodiments, there is provided a photovoltaic device comprising: a front substrate; a front substantially transparent conductive electrode; an absorber semiconductor film; a conductive and reflective rear electrode; a rear glass substrate that supports at least the rear electrode; and wherein the rear electrode comprises a first layer comprising an oxide of Mo and a second conductive layer comprising substantially metallic Mo provided on the rear glass substrate over at least the first layer, so that the first layer comprising the oxide of Mo is located between the rear glass substrate and the second layer comprising substantially metallic Mo.
In certain example embodiments, there is provided method of making a rear electrode structure for a photovoltaic device, the method comprising: providing a glass substrate; depositing a conductive electrode on the glass substrate, and then ion beam treating a major surface of the electrode in order to texture, or additionally texture, the major surface of the electrode thereby providing a textured electrode having a textured reflective surface; and using the textured electrode, supported by at least the glass substrate, as a rear electrode in a photovoltaic device.
In certain example embodiments, there is provided a method of making a photovoltaic device, the method comprising: providing a glass substrate; depositing a conductive electrode comprising Mo on the glass substrate, and then texturing a major surface of the electrode comprising Mo thereby providing a textured electrode comprising Mo having a textured reflective surface; and using the textured electrode comprising Mo, supported by at least the glass substrate, as a rear electrode in a photovoltaic device.